Due to worldwide attention to environment pollution and regulations of CO2, there is a need to develop eco-friendly vehicles. As a result, there has been a growing interest in a fuel cell vehicle which is eco-friendly and excellent in efficiency in order to replace an internal combustion engine vehicle which causes environmental pollution.
Among fuel cells for a vehicle, a polymer electrolyte membrane fuel cell has been drawn most attention. The polymer electrolyte membrane fuel cell has higher efficiency, current density, output density, and a shorter starting time, and uses a solid electrolyte to prevent corrosion. Further, there is no need to control an electrolyte.
The polymer electrolyte membrane fuel cell generates electrical energy while generating water and heat by an electrochemical reaction of a fuel including hydrogen with an oxidizer such as air, in which a supplied fuel is separated into hydrogen ions and electrons at a catalyst of an anode electrode, and then, the separated hydrogen ions move over a cathode electrode through a polymer electrolyte membrane. In this case, the oxidizer is combined with the electrons which move along an external wire to generate the electrical energy while supplying water.
In the actual fuel cell for a vehicle, an individual unit cell needs to be stacked as much as required potential to obtain high potential.
In general, to operate the fuel cell stacks after assembling the fuel cell stacks which are an essential component of a fuel cell vehicle, a need exists for a process of activating a stack to secure a triple phase boundary (TPB), remove impurities of the polymer electrolyte membrane or the electrode, and improve ion conductivity of the binder and the polymer electrolyte membrane.
In particular, after the fuel cell stacks are assembled, the activity is reduced in the electrochemical reaction at the time of an initial operation. Therefore, a process of activating a fuel cell stack needs to be carried out to secure a normal initial performance of the fuel cell stack.
The process of activating a fuel cell stack is called pre-conditioning or break-in. Here, the process of activating a fuel cell stack is to activate a catalyst which does not participate in the reaction and sufficiently hydrate the electrolyte included in the electrolyte membrane and the electrode to secure a hydrogen ion passage.
Generally, to activate the fuel cell electrode membrane, various activation protocols such as constant potential, constant current, and a pulse current under high humidity conditions have been developed. A recent method for activating a fuel cell stack which has been mainly used is a method of repeatedly performing a process of discharging high current density (1.2 or 1.4 A/cm2) for 30 seconds and a process of performing a pulse discharge for 2 to 3 minutes in a shut-down condition. However, the activation method based on a pulse needs to use an electric load to apply a high current load and greatly increases a consumed quantity of hydrogen.
In the activation process as described above, a usage time of the activation equipment (including the electric load) is equal to or more than about 90 minutes, and the consumed quantity of hydrogen is equal to or more than 1.7 kg based on a sub-module. However, if the production of the fuel cell stack increases in future, the stack activation may be a bottle neck making the total production speed of the fuel cell stack slow due to the limitation of the stack activation equipment.
Further, a method for achieving partial activation by directly supplying hydrogen and a droplet into the cathode of the stack and a method for additionally achieving complete activation by partial activation using an electric load and storage have also been used. These methods need to use the electric load in the partial activation process or the additional activation process. The hydrogen adsorption method directly supplies hydrogen and a droplet from the outside into the cathode, and therefore, the hydrogen adsorption method has a disadvantage in that there is a need to change a pipe and the hydrogen is not adsorbed onto a surface of platinum of the cathode adjacent to the membrane well.